The present invention relates to arrangements for coupling a cable to a circuit board. More particularly, the present invention relates to non-detachable cable-to-board arrangements that offer improved strain relief, reduced thickness, improved RF shielding, and simplified manufacture.
Modem electronic equipments such as computers or consumer/commercial electronics typically include one or more circuit boards on which electronic devices are populated. To furnish power and/or signals to the circuit board, one or more cables having therein one or more wires may be coupled to the circuit board. There are in the current art many techniques for connecting the wires of a cable to the circuit board. One simple technique involves manually separating, aligning, and directly soldering the individual wires of a cable with individual pads on the circuit board. There are, however, many disadvantages with this approach. By way of example, the manual separation, alignment, and soldering of individual wires with individual pads on the circuit board is a laborious and time-consuming, and therefore expensive, process. Further, as the size of the circuit board shrinks, the pads themselves and the distance that separates one pad from its neighbor also shrink, making it difficult to accurately align and solder the individual wires with the miniaturized pads. Still further, the electrical connections formed by this method tend to be unreliable since the soldered joints and the pads themselves are subjected to the mechanical stress that is generated as the cable is flexed and/or pulled during use.
To improve the mechanical strength of the coupling and improve manufacturability, connectors may be interposed between the cable and the circuit board. FIGS. 1A and 1B show a prior art technique for coupling a cable 102 to a circuit board 104 through a cable-side connector 106 and a board-side connector 108. Cable-side connector 106 is typically a plastic connector having therein a plurality of contacts. The contacts in cable-side connector 106 are soldered or crimped onto individual wires of cable 102. Similarly, board-side connector 108 includes a plurality of corresponding contacts, which are electrically coupled with pads of circuit board 104. The contacts of board-side connector 108 are configured to mate with the contacts of cable-side connector 106 when cable-side connector 106 is inserted into board-side connector 108 to form the desired electrical connections.
To relieve stress on the connectors, cable-side connector 106 may be provided with a strain-relief portion which reduces the stress experienced by the connectors when the cable is suddenly flexed during use. Cable-side connector 106 is also shown having a latch 110, which mates with a corresponding depression built into board-side connector 108 when the connectors are coupled. Latch 110 prevents the connectors from being inadvertently pulled apart when cable 102 is inadvertently pulled away from the circuit board during use. On the other hand, the connectors may be separated if latch 110 is appropriately depressed or manipulated prior to pulling the connectors apart.
Although the detachable connector arrangement of FIGS. 1A and 1B represents an improvement over the above-discussed method of simply soldering the wires directly to the pads of the circuit board, there are also disadvantages. By way of example, the detachable arrangement of FIGS. 1A and 1B requires two connectors, which increases cost. The use of a board-side connector 108 also increases the thickness of the cable-to-board arrangement, rendering it difficult to contain the circuit board in thin cases. Further, the mating contacts within cable-side connector 106 and/or board-side connector 108 tend to be deformed, oxidized and/or contaminated with dirt over time, thereby increasing the contact resistance or in many cases, failing to maintain the electrical connections altogether. Additionally, after cable-side connector 106 is mated with board-side connector 108, there is little flexibility in the vertical direction (i.e., in the direction orthogonal to the plane of the circuit board) beyond what the strain relief may offer. The rigidity of this coupling may sometimes causes board-side connector 108 to be detached from circuit board 104 when cable 102 is flexed. This detachment may occur as the contacts of the board-side connector are separated from the pads of the circuit board. More likely, the detachment may occur as the pads themselves are lifted from the surface of the circuit board, which may break the connections between the pads and the conductive traces on the circuit board.
To address the deficiencies associated with the detachable arrangement of FIGS. 1A and 1B, the connectors may of course be made non-detachable. FIGS. 2A/2B illustrate another arrangement for coupling wires of a cable to pads on a circuit board wherein the coupling between the connectors is made non-detachable by the user to increase reliability. With reference to FIGS. 2A/2B, circuit board 104 is again shown connected to board-side connector 108. Cable 102 is coupled to strained relief 200, which is interpose between an opening in case 206 and cable 102 to offer some protection to components within case 206 from mechanical stress when cable 102 is flexed. Wires 204 of cable 102 is coupled to a cable-side connector 106, typically by a soldering or crimping process. With case 206 open, cable-side connector 106 is inserted in board-side connector 108 and tested to ensure that the proper electrical connections are made. Afterward, case 206 is closed, essentially preventing user access to the connectors to render them non-detachable from the user's perspective.
Although the arrangement of FIGS. 2A/2B addresses many of the reliability issues associated with detachable connectors, there are also disadvantages. By way of example, the arrangement of FIGS. 2A/2B requires the use of a board-side connector 108, which unnecessarily increases manufacturing cost. Further, board-side connector 108 and/or cable-side connector 106 are physical apparatus with nontrivial heights. As electronic equipment becomes smaller and the thickness of case 206 decreases, these connectors may not fit properly within case 206. By way of example, the circuit board of PC cards (also known as PCMCIA cards) are encapsulated in shells or cases that may be as thin as 5 mm. In many cases, the use of these connectors causes bulges in the housing of the case or prevents the closing of the case altogether. This problem is exacerbated by the fact that individual wires 204 typically need to have some nontrivial minimum length for handling during the crimping or soldering operation that couples wires 204 onto cable-side connector 106. The wires 204 may then need to be coiled within case 206 prior to closing the case, further exacerbating the case protrusion problem.
Additionally, it is found that prior art arrangements fail to adequately shield the circuitries internal of the case halves (i.e., within the shell), thereby allowing electromagnetic emission to emanate therefrom through gaps or openings in the shell. With reference to FIG. 1, for example, although the board-side connector is present in the shell opening 118 where the board-side connector is disposed, a substantial portion of the board-side connector is formed of a non-metallic material, which provides poor RF shielding. Side 120 of the case where the board-side connector is disposed is also typically the side exposed to the outside world for access to the board-side connector. Thus, poor RF shielding along this side of the case (e.g., side 120 in FIG. 1B) tends to be more detrimental to the overall acceptability of the electronic device from an electromagnetic emission standpoint.
In view of the foregoing, there are desired improved cable-to-board arrangements that offer improved strain relief, reduced thickness, improved RF shielding and ease of manufacture.